Hydroxyl-terminated chloroprene polymers

ABSTRACT

Substantially linear chloroprene polymers terminated by hydroxyalkyl xanthate or hydroxycycloalkyl xanthate groups are obtained by photopolymerizing chloroprene, optionally in admixture with other comonomers, in the presence of xanthogen disulfides terminated by hydroxyalkoxy or hydroxycycloalkoxy groups. These xanthogen disulfides are made by reaction of carbon disulfide with suitable diols, followed by oxidation of the resulting xanthates. The chloroprene polymers of the present invention can be chain-extended by reaction with polyisocyanates to solid, rubbery materials and also can be used to make polyurethane foams.

United States Patent Takeshita Aug. 19, 1975 [54] HYDROXYLJFERMINATED3,580,830 5/1971 Siebert 260/79 3619226 ll/l97l Hargreaves et al. 260/79CHLOROPRENE POLYMERS [75} Inventor: Tsuneichi Takeshita, Newark, Del.

[73] Assignee: E. l. Du Pont de Nemours and Company, Wilmington Del.

[22] Filed: Apr. 2, i974 [2]] Appl. No.: 457,387

[52] US. Cl. 204/159.24; 204/l59.l5; 204/l 59.]8; 260/775 CR; 260/775AP; 260/79; 260/923; 260/455 B [51] int. Cl. C08f His [58] Field ofSearch 260/79, 77.5 CR, 77.5 AP, 260/923; 204/[5924 [56) ReferencesCited UNITED STATES PATENTS 1047544 7/1962 Byrd 260/79 PrimaryExaminerMelvyn l. Marquis [57] ABSTRACT Substantially linear chloroprenepolymers terminated by hydroxyalkyl xanthate or hydroxycycloalkylxanthate groups are obtained by photopolymerizing chloroprene,optionally in admixture with other comono mers. in the presence ofxanthogen disulfides terminated by hydroxyalkoxy or hydroxycycloalkoxygroups These xanthogen disulfides are made by reaction of carbondisulfide with suitable diols, followed by oxidation of the resultingxanthates. The chl0roprene polymers of the present invention can bechainextended by reaction with polyisocyanates to solid, rubberymaterials and also can be used to make polyurethane foams.

7 Claims, N0 Drawings HYDRUXYL-TERMINA'IIII) 'III,( )R( )IRENI",POLYMERS 'l'his invention relates to a substantially linear chloroprenepolymer which is terminated by hydroxyalkyl xanthate orhydroxycycloalkyl xanthate groups.

('hloroprcnc polymers terminated by functional groups are known. 'lhus.for example. US. Pat No. 2.877.2l2 teaches the poIymeri/ation ofchloroprcnc in the presence of an aliphatic :midicarhoxylate in whichthe carbons attached to the an: group are tertiary. 'lhis azo compoundis a polymerization initiator. which uner the polymerization conditionsforms free radicals. 'l'he resulting polymer thus is terminated bycarboxylate groups attached to the polymer chain through a tertiarycarbon atom. 'l'hese carboxylate groups can be reduced to hydroxylgroups. The patent further discloses that in the presence of hydrogenper oxide chloroprene polymerilcs to a hydroxylterminated product.However. the efficiency of this reaction. i.e.. the resultingfunctionality of chloroprenc polymer is not discussed. and the polymerrequires extensive washing to remove impurities US. Pat. No. 3.580.830discloses the preparation of xanthateterminated polymers. wherein thexanthate termination is essentially complete. that is. a xanthate groupis present at each end of the polymer chain. While many monomers aresaid to undergo this reaction. chloroprcne is not specificallymentioned. However. polymerization of chloroprene in the presence ofdialkyl xanthogcn disullides. which serve as chain transfer agents. alsois known. The xantliate groups are not further reactive and normallywould have to he converted to reactive groups. such as mercaptan. tomake possible a further chain extension. Normally some functionality islost during these conversion reactions.

(hloroprene polymers. especially liquid polymers, hearing a reactivefunctional group at each end of the molecule. that would be cured with apolyfunctional vulcanizing agent at room temperature and could heobtained directly as the product of an economical onestep polymerizationprocess would be very desirable in the preparation of caulks andadhesives.

SUMMARY ()l" 'I'Hli lNVliN'l'lUN According to the present invention.there is now provided a substantially linear chloroprene polymer. whichis terminated at each end of the chain by a xanthate group representedby the following formula l )3 wherein A is an alkanediyl oreycloalkanediyl radical having at least two carbon atoms. and u is apositive integer of at least I. lhe two valcnces of A must not beattached to the same carbon atom or to two tertlary carbon atoms.

The polymers of this invention are made by a direct process. which doesnot require additional SlLtts to pro vide the desired terminalfunctionality.

Suitable divalent alkyl and cycloalkyl radicals. A. in

(ill

Formula l include l.2-ethanediyl (or ethylene). l.2- propanediyl (orLlpropylenc. etc.). l.3-propanediyl. l.4-butanediyl. lfi-butancdiyl.l.()hL'XZIHCLll) l. 2.5- hexanediyl. l.2-dodecanediyl. and 1.4-cyclohexanediyl. When n is l. the preferred divalent radical A isIAJiutanediyl or l.(i-hexanediyl. It is not considered economicallyattractive to allow the radical A to have more than twelve carbon atoms.When n is larger than l. it is preferred to maintain the size of Awithin the range of 2-4 carbon atoms.

Although there is no theoretical ground to limit the value of u. it isnot practical to exceed the value of 4 because of added cost. which isnot justilied by any pos sible improvement in the properties of thematerial.

The polymers of the present invention are prepared by a photoinitiatedpolymerization. using an ultraviolet light source. substantially inagreement with the pro cess of the above-mentioned US. Pat. No.3.580.830. The specific polymerization conditions are especiallydescribed in (olumn 3. line 23 to column 4. line 15 of said patent.However. instead of conventional dialkyl xanthogen disullides. thexanthogen disullides used in the process of the present invention havethe following formula (2):

wherein A and u have the above-defined meaning The xanthogen disullidcs(2) useful in the present invention are made by reaction ofa suitablediol with carhon disullide followed by oxidation of the resultingxanlhates. for example. with ammonium persulfate. Suitable diolsinclude. for example. ethylene glycol. propylene glycol, diethyleneglycol. methylene glycol. tetraethylene glycol, l.4-butanediol.l.3-butanediol. 2.5-hexanediol, l.4-cyclohexanediol and L2-dodecanediol. The reaction of carbon disullide with a diol is carriedout in the presence of sodium hydroxide at low temperatures. about|0l5(. The oxidation step also is conducted below about I5(. While nodiluent is necessary for lower diols. it is practical to dilute thereaction mixture with water when a higher diol such as Lo-hexanediol isused. Otherwise. the reaction mixture may solidify at the lowertemperature.

The reaction product is usually recovered by extraction with a suitablesolvent. for example. methylene chloride. and evaporation of thesolvent. It is heated at 0 l 0C to minimize decomposition. Yields are inmost cases in the range of 75-95%.

Polymerization of chloroprene in the presence of the xanthogendisullides having formula (2) can be carried out in hulk ehloroprene orin solution in a solvent such as ethylene dichloride or in aqueoussuspension or in emulsion. The reaction is preferably carried out below50(' to minimize undesirable side reactions. which could lead tobranching or unreactive end groups. Practical rates of polymerizationcan he maintained above l0(. while a convenient upper temperature limitwill be about 25"(.

The xanthogen disullide will normally be present in the polymerizationmedium at a concentration of about (MU to 5.0 mole percent based on thetotal monomers. Lower concentrations. for example 0.0} 0.3 mole percent.would normally lead to solid polymers; between .1 5 and 5 mole percent.lluid polymers are obtained.

Between 0.3 and 2.5 mole percent. the polymer products change from softsolids to viscous fluids as the con centration is increased over thisrange. These xanthogen disulfides will function as chain transfer agentsboth in the process of this invention and in any conventional freeradical initiated polymerization.

In addition to chloroprene homopolymers. copolymers of chloroprenecontaining up to about 50 weight percent of other copolymerizablemonomers are within the scope of this invention. Therefore. the termchloroprene polymer will be construed to include both such homopolymersand copolymers. Representative comonomers which can be copolymerizedwith chloroprene include, for example. methyl or ethyl acrylate andmethacrylate. acrylonitrile. styrene, vinyl acetate. butadiene, isopreneand 2.3-dichloro-1,4-butadiene. it is often desirable to incorporateabout weight per cent of 2.3-dichloro-l .4-butadiene in liquidchloroprene polymers to impart freeze resistance.

The hydroxylterminated chloroprene polymers of the present invention arereadily curable at ambient temperature with polyfunctional isocyanates,such as, for example, 2.4-and/or 2,6- diisocyanatomethylbenzene and 4,4-diisocyanatodiphenylmethane. Other polyfunctional compounds which reactwith hydroxyl groups include. for example. polyfunctional acid chloridessuch as terephthaloyl chloride and polyfunctional carbodiimides.

These novel polymers thus are useful in two-part adhesives or caulkingcompounds utilizing curing agents. They also are useful in thepreparation of polyurethane foams, where they would replace all or partof the conventional polyols in the formulation. For these applications.liquid hydroxyl-terminated chloroprene polymers are usually moredesirable than the solid polymers.

This invention is now illustrated by representative examples of certainpreferred embodiments thereof, where all proportions. parts andpercentages are by weight unless otherwise indicated.

EXAMPLE l Photopolymerization of l-chlorobutadiene and2,3-dichlorobutadiene in aqueous suspension in the presence of4-hydroxybutyl xanthogen disulfide.

A. Preparation of 4-hydroxyhutyl xanthogen disulfide To a mixture of 360g of 1,4-butanedio] and 30 g of carbon disulfide. placed in a ZO-roundbottomed flask. was added with stirring at 5l()C over a period of about1 hour a sodium hydroxide solution obtained by dissolving 6.5 g ofsodium hydroxide in ml of water. Subsequently, the solution wascontinuously stirred for 2 hours at room temperature. After diluting themixture with 200 ml of water, 51 g of ammonium persulfate dissolved in80 ml of water was added in about minutes. maintaining the temperatureat about 17C. After adding about 500 ml of water. the organic layer wasextracted with methylene chloride. dried over sodium sulfate and freedfrom the solvent. to give 60.2 g of yellow. viscous oil. Since the crudeproduct still contained 1 3"? volatiles on vacuum desiccation. theoverall yield was 8U); based on the weight of carbon disulfide charged.The product was filtered and stored in a refrigerator. The infraredspectrum showed the presence of both OH and xanthate groups.

B. Polymerization A stirred mixture of 90 g of chloroprene. l() g of2.3- dichlorobutadiene. 13.6 g of 4-hydroxybutyl xanthogen disulfide,and 500 ml of water was irradiated for 7 hours at 1926C using a GE H-A3mercury lamp (main emission at =36O nm). The monomer layer, which wasinitially lighter than water, was converted to a fluid polymer heavierthan water. The organic product was collected by extraction withmethylene chloride, which yielded 52.5 g of yellow viscous fluid onremoval of the solvent. The monomer conversion was 39%. In order toobtain analytical samples. the product was purified by precipitatingfrom benzene solution with methanol. Forty-one grams of the purifiedproduct was stabilized with 0. l g of an antioxidant. Number averagemolecular weight, M (by vapor phase osmometry, VPO), 6.400; S, 2.8%; Cl,40.4%; 0, 1.42%; n 0.13. Infrared spectroscopy showed the presence of 4-hydroxybutyl xanthate ester end groups as well as the C#: band due topolychloroprene. A sufficiently satisfactory bifunctionality wasdemonstrated by a dissocyanate chain extension of the fluid product intoa snappy solid rubber as described in Example 4.

EXAMPLE 2 Photopolymerization of chloroprene in aqueous emulsion in thepresence of 4hydroxybutyl xanthogen disulflde Chloroprene wasphotopolymerized in a manner sim ilar to that of Example l except thatirradiation was carried out in aqueous emulsion. The emulsion consistedof a solution of 50 g of 4-hydroxybutyl xanthogen disulfide in 300 g ofchloroprene dispersed in a solution of 10 g of Ultrawet 60L in 330 ml ofwater. Dispersion was formed by mixing the chloroprene and watersolutions together with high speed agitation. After 13 hours irradiationat l623C, the product was isolated by breaking the latex with amethanol-calcium chloride-water solution. A viscous fluid polymer (85.4g) was obtained. On standing, the fluid sample hardened due tocrystallization. M. (VPO) 3.830; S, 4.4%; O, 2.02%; 1 0.15.

EXAMPLE 3 Photopolymerization of chloroprene and 2.3-dichlorobutadienewith 4-hydroxybutyl xanthogen disulfide in solution Chloroprene (340 g)and 60 g of 2.3- dichlorobutadiene were photopolymerized at l528C in asolution containing 360 ml of ethylene dichloride and 68 g of4-hydroxybutyl xanthogen disulfide in a manner similar to that ofExample 1. After 21 hours irradiation and removal of the solvent. 354.1g of brown-colored fluid polymer was obtained. After purification withmethanol as described in Example 1, the liquid sample was analyzed. TX(VPO) 3.400; S. 3.9%; O, 1.86%;17 0.1 1; C]. 39.5%.

EXAMPLE 4 Curing with a diisocyanatomethylbenzene Two-gram portions ofthe fluid 4-hydroxybutyl Xanthate ester-terminated chloroprene polymerobtained in Example 1 were treated with increasing proportions of HyleneT Organic lsocyanate (Du Ponts mixture of 2,4- and2.o-tolylenediisocyanate) in the presence of a tin catalyst. T-12 (Metaland Thermit Corporation). The stocks of the Hylene T/chloroprene polymerratios of 0.040.07/2.0 gave a snappy rubbery product after standingseveral days at room temperature. The final nvalues measures in benzeneor chloroform (98l00% soluble) were 0.52-0.62 in contrast to theoriginal value of 0.13 for the starting fluid xanthate esterterminatedpolymer. One slab sample prepared at the Hylene T/Fluid ratio of 007/showed a tensile strength of 900 lb/in v EXAMPLE 5 Preparation of foamsForty-five grams of the fluid copolymer prepared in Example 3 was usedto prepare a foam by reaction with 22 g of Hylene T, 5 drops of T-12,0.5 g of 1,6- hexanediol, 0.5 g of QuadrollN.N,N',N-tetrakis( 2hydroxypropyl)ethylenediamine] (BASF Wyandotte Corporation). 1 g ofL-520 silicone fluid (Union Carbide Corporation), 1 g ofEPON" 828, and1.8 ml of 5% aqueous solution ofDabco". The density of the foam was 2.43lb/ft". The load-bearing capacity of the foam at 50% deflection was 0.44lb/in EXAMPLE 6 Photopolymerization of 2-chlorobutadiene and2,3-dichlorobutadiene in aqueous suspension in the presence of2-(2-hydroxyethoxy)-ethyl xanthogen disulfide.

A. Preparation of 2-(2-hydroxyethoxy)ethyl xanthogen disulfide Using theprocedure of Example IA, the xanthate was prepared from 800 g ofdiethylene glycol, 19] g of carbon disulfide, and 100 g of sodiumhydroxide and oxidized to the disulfide with 312 g of ammoniumpersulfate. The product was extracted into 400 ml of methylene chlorideand the excess diol removed by washing three times with 1 liter ofwater, where each washing involved stirring continuously for 5 min. Themethyl ene chloride solution was dried with magnesium sulfate and thesolvent removed under vacuum to give 374 g of a clear amber oil, an 82%yield based on carbon disulfide. Sulfur analysis: found, 35.9%;expected, 35.4%. The infrared spectrum showed the presence of both OHand xanthate groups.

B. Polymerization A solution of 191 g of Chloroprene, 47 g of 2,3-dichlorobutadiene, and 29 g of 2-hydroxyethoxy)-ethyl xanthogendisulfide in 200 ml of methanol was stirred under N in a Pyrex" vesselwhile being irradiated for 7.8 hours in a Rayonet Model RPR 100Photochemical Reactor, Southern New England Ultraviolet Company,Middletown, Ct. with the light from 16 8-watt lamps emitting princi allyat 300 nm. The polymer was not soluble in the reaction medium andprecipitated as it formed. After decanting the solvent and washing theprecipitated product with methanol, it was dissolved in 150 ml ofmethylene chloride and dried with magnesium sulfate. Removing thesolvent gave 52 g ofa clear. pale yellow. lluid polymer. M,, (VPO) 6830;S. 1.8% monomer conversion 21%.

EXAMPLE 7 Photopolymerization of l-chlorohutadiene and2.3dichlorobutadiene in aqueous suspension in the presence ofZ-hydroxy-l-propyl xanthogen disulfide A. Preparation of2-hydroxy-1-propyl xanthogen disulfide By the procedure of Example 6A.the xanthate was prepared from 468 g of 1,2-propanediol, 234 g of carbondisulfide and 123 g of sodium hydroxide and oxi' dized to the disulfidewith 380 g of ammonium persulfate. The isolated product was 325 g of aclear yellow oil, yield based on carbon disulfide. Sulfur analysis:found 42.9%; expected, 42.4%. The product was stored in a freezer. Theinfrared spectrum showed the presence of both OH and xanthate groups.

B. Polymerization Chloroprene (477 g) and 62 g of 2,3- dichlorobutadienewere photopolymerized at 2141C in a solution containing 250 ml ofethylene dichloride and 61 g of Z-hydroxy-l-propyl xanthogen disulfidein the manner described in Example 1. After 10 hours of irradiation, theconversion of monomers was 56%. Removal of solvent and unreactedmonomers and purification with methanol as in Example 1 gave 269 g of afluid polymer. M (VPO) 3630; S, 3.3%; Brookfield viscosities, 2.5 X 10cps; Cl, 39.0%.

EXAM PLE 8 Photopolymerization of 2-chlorobutadiene and2,3-dichlorobutadiene in aqueous suspension in the presence of6-hydroxy-1-hexyl xanthogen disulfide A. Preparation of6-hydroxy-l-hexyl xanthogen disulfide The procedure of Example 6A wasused to prepare the xanthate from a mixture of 200 ml of water and 460 gof 1,6-hexane diol, 81.5 g of CS and 42.6 g of sodium hydroxide and tooxidize the xanthate to the disulfide with 133 g of ammonium persulfate.A clear yellow oil weighing 151 g and representing a yield of 73% wasobtained. Analysis; found, 33.1% S; expected 33.2% S. The infraredspectrum showed the presence of both OH and xanthate groups.

B. Polymerization Chloroprene (600 g), 93 g of 2,3-dichlorobutadiene,and 78 g of o-hydroxy-l-hexyl xanthogen disulfide were irradiated for 7hours at 2137C as described in Example 1, which gave 46% conversion ofthe monomers. Removal of unreacted monomers and purification withmethanol as in Example 1 gave 352 g of a yellow fluid polymer. M,, (VPO)5190; S, 1.9%.

The trade names used in the above Examples have the following meaning:

Dabco, Air Products and Chemicals triethylenediamine Epon 828 Resin,Shell Chemical Company 2,2-bis(p-glycidoxyphenyl) propane SiliconeSurfactant L-520, Union Carbide a water-soluble block copolymer of asilicone and polyether T-lZ, Metal & Thermit Corporation dibutyltindilaurate Ultrawet 60L Surfactant. ARCO Chemical Companytriethanolammonium dodecylbenzenesulfonate.

I claim:

1. A substantially linear polymer of chloroprene containing 050 weightpercent of at least one copolymerizable monomer. said polymer beingterminated substantially at each end of the chain by a xanthate grouphaving the following formula wherein A is an alkanetliyl orcyeloalkanediyl radical having at least two carbon atoms. and n is apositive integer of l-4; with the proviso that the two valences of A areattached to different carbon atoms only one of which can he a tertiarycarbon atom.

2. A polymer ol'claim I wherein n is l and the radical A has at most 12carbon atoms.

3. A polymer ofclaim I wherein n is 2-4, and the rad ieal A has at most4 carbon atoms.

4. A polymer ofclaim 2 wherein A is l,4-hutancdiyl LZ-ethanediyl.lbhexanediyl or LZ-propanediyl.

5. A process for preparing a polymer ofehloroprene containing (l-SUweight percent of at least one copoly merizahle monomer, said polymerbeing terminated substantially at each end of the chain by a xanthategroup having the following formula wherein A is an alkanetliyl orcyeloalkanediyl radical having at least two carbon atoms. and n is apositive intill wherein A and n have the above-defined meanings; andcarrying out the polymerization at about l()-SUC.

6. The process of claim 4 wherein the proportion of the xanthogendisult'ide is 2.5-5 mole percent based on total monomers.

7. A polyurethane in which the polyol component is a chloroprene polymerof claim I.

1. A SUBSTANTIALLY LINEAR POLYMER OF CHLOROPRENE CONTANING 0-50 WEIGHTPERCENT OF AT LEAST ONE COPOLYMERIZABLE MONOMER, SAID POLYMER BEINGTERMINATED SUBSTANTIALLY AT EACH END OF THE CHAIN BY A XANTHATE GROUPHAVING THE FOLLOWING FORMULA
 2. A polymer of claim 1 wherein n is 1 andthe radical A has at most 12 carbon atoms.
 3. A polymer of claim 1wherein n is 2-4, and the radical A has at most 4 carbon atoms.
 4. Apolymer of claim 2 wherein A is 1,4-butanediyl, 1,2-ethanediyl,1,6hexanediyl or 1,2-propanediyl.
 5. A process for preparing a polymerof chloroprene containing 0-50 weight percent of at least onecopolymerizable monomer, said polymer being terminated substantially ateach end of the chain by a xanthate group having the following formula6. The process of claim 4 wherein the proportion of the xanthogendisulfide is 2.5-5 mole percent based on total monomers.
 7. Apolyurethane in which the polyol component is a chloroprene polymer ofclaim 1.